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Makings of a deadly brown cloud

Burn­ing or­gan­ic ma­ter­ial for home use is large­ly res­pon­sible for a haze over south Asia, re­search­ers re­port.

Jan. 22, 2009
Courtesy Science
and World Science staff

Dur­ing win­ter, an im­mense, un­healthy brown cloud of soot hangs over South Asia and the In­di­an Ocean. Re­search­ers have won­dered ex­actly what makes up the haze—soot from burn­ing or­gan­ic ma­te­ri­al or from burn­ing fos­sil fu­els?

Now, sci­en­tists re­port that burn­ing bi­o­mass, or­gan­ic mat­ter like wood and dung, con­tri­butes two-thirds of the soot in these clouds.

A brown haze near Pu­ne, In­dia, near a sam­pling site where re­search­ers col­lect­ed "brown cloud" par­t­i­cles for anal­y­sis. (Im­age cour­te­sy AAAS/Science)


This find­ing im­plies that lim­it­ing bi­o­mass com­bus­tion, par­tic­u­larly the small-scale burn­ing of wood and dung for home heat­ing and cook­ing, will be im­por­tant to im­prove air qual­ity in the re­gion, ac­cord­ing to the in­ves­ti­ga­tors.

Ör­jan Gustafs­son of Stock­holm Uni­ver­s­ity in Swe­den and col­leagues used mea­sure­ments of at­mos­pher­ic soot par­t­i­cles gath­ered on a moun­tain­top in west­ern In­dia and on the is­land of Mal­dives for the stu­dy.

Their find­ing makes it clear that ef­forts should­n’t be lim­it­ed to car traf­fic and coal-fired pow­er plants, the sci­en­tists said. In­stead, they rec­om­mend fight­ing po­verty and spread­ing green tech­nol­o­gy to lim­it emis­sions of soot from small-scale bi­o­mass burn­ing.

The soot raises can­cer risk, and can be traced to the deaths of many peo­ple in Chi­na and In­dia from car­di­o­vas­cu­lar and res­pi­ra­to­ry dis­eases, ac­cord­ing to the group. But be­cause the soot par­t­i­cles only stay in the at­mos­phere for days or weeks at a time, there is hope the prob­lem will clear up quickly once the causes are ad­dressed. The find­ings are pub­lished in the Jan. 23 is­sue of the re­search jour­nal Sci­ence.


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During winter, an immense, unhealthy brown cloud of soot hangs over South Asia and the Indian Ocean. Researchers have wondered exactly what it was made of—soot from burning organic material or from burning fossil fuels? Now, scientists report that burning biomass, organic matter like wood and dung, contributes two-thirds of the soot in these clouds. This finding implies that limiting biomass combustion, particularly the small-scale burning of wood and dung for home heating and cooking, will be important to improve air quality in the region, according to the investigators. Örjan Gustafsson of Stockholm University in Sweden and colleagues used measurements of atmospheric soot particles gathered on a mountaintop in western India and on the island of Maldives for the study. Their finding makes it clear that efforts shouldn’t be limited to car traffic and coal-fired power plants, the scientists said. Instead, they recommend fighting poverty and spreading green technology to limit emissions of soot from small-scale biomass burning. The soot raises cancer risk, and can be traced to the deaths of many people in China and India from cardiovascular and respiratory diseases, according to the group. But because the soot particles only stay in the atmosphere for days or weeks at a time, there is hope the problem will clear up quickly once the causes are addressed. The findings are published in the Jan. 23 issue of the research journal Science.